Francesca Santilli

Soluble Forms of RAGE in Human Diseases: Clinical and Therapeutical Implications

The ligand - receptor for advanced glycation end-products (RAGE) axis has emerged as a novel pathway involved in a wide spectrum of diseases, including diabetes mellitus, atherothrombosis, chronic renal failure, rheumatoid arthritis, neurodegeneration, cancer and aging. Circulating soluble forms of RAGE (sRAGE), arising from receptor ectodomain shedding and splice variant [endogenous secretory (es) RAGE] secretion, may counteract RAGE-mediated pathogenesis, by acting as a decoy. Several studies suggest that decreased levels of sRAGE and/or esRAGE may be useful as a biomarker of ligand-RAGE pathway hyperactivity and inadequate endogenous protective response, thus providing a powerful complement to cardiovascular risk stratification and an interesting target of therapeutic interventions. This review will focus on the pathophysiological determinants of soluble forms of RAGE in different clinical settings, with particular reference to the mechanisms involved in their generation and clearance, the association with cardiovascular risk factors, the interplay with low-grade inflammation, oxidative stress and endothelial dysfunction, and the possible pharmacological modulation of their plasma levels.

Enhanced Lipid Peroxidation and Platelet Activation in the Early Phase of Type 1 Diabetes Mellitus Role of Interleukin-6 and Disease Duration

Background—To investigate early events possibly related to the development of diabetic angiopathy, we examined whether 8-iso-prostaglandin F2&agr; (8-iso-PGF2&agr;) formation, a marker of in vivo oxidant stress, is altered in different stages of type 1 diabetes (T1DM) and whether it correlates with the rate of thromboxane (TX) A2 biosynthesis, a marker of in vivo platelet activation. We also investigated the relationship between inflammatory markers and F2-isoprostane formation in this setting. Methods and Results—A cross-sectional study was performed in 23 insulin-treated patients aged <18 years with new-onset T1DM (≤6 weeks, group A), matched for age and gender with 23 patients with stable disease (>1 year, group B). Urinary 8-iso-PGF2&agr; and 11-dehydro-TXB2 were measured in all patients and in age- and gender-matched controls. Circulating interleukin-6 (IL-6), tumor necrosis factor-&agr;, and C-reactive protein were also determined as markers of the inflammatory response. Fifteen of the 23 children in group A were reexamined after 12 months. Compared with either controls or group B, diabetic children in group A showed significantly higher levels of 8-iso-PGF2&agr;, 11-dehydro-TXB2, IL-6, tumor necrosis factor-&agr;, and C-reactive protein. Statistically significant correlations between IL-6 and both 8-iso-PGF2&agr; (r =0.63, P <0.001) and 11-dehydro-TXB2 (r =0.51, P <0.01) were observed. The 15 patients reexamined after 1 year showed a significant reduction in lipid peroxidation and platelet activation (P <0.02 and P <0.001, respectively), consistent with reduced levels of IL-6 and tumor necrosis factor-&agr;. Conclusions—These results demonstrate that enhanced lipid peroxidation and platelet activation represent early events in T1DM that are possibly related to an acute inflammatory response. These noninvasive indexes may help in further examining T1DM pathophysiology and monitoring pharmacological interventions to interfere with disease development and progression.

Soluble forms of RAGE in internal medicine

The receptor for advanced glycation end-products (RAGE) and its ligands are intimately involved in the pathobiology of a wide range of diseases that share common features, such as enhanced oxidative stress, immune/inflammatory responses, and altered cell functions. Soluble forms of RAGE (sRAGE), including the splice variant endogenous secretory (es)RAGE, have been found circulating in plasma and tissues. Experimental data suggest that these isoforms may neutralize the ligand-mediated damage by acting as a decoy. Moreover, evidence is mounting to support a role for both sRAGE and esRAGE as biomarkers or endogenous protection factors against RAGE-mediated pathogenesis. In this review, we will focus on clinical and therapeutical implications arising from studies investigating the significance of soluble RAGE isoforms in several clinical settings, including cardiovascular disease, diabetes mellitus, hypercholesterolemia, chronic renal failure, immune/inflammatory diseases, pulmonary diseases, neurodegeneration, and cancer.

Role of Growth Factors in the Development of Diabetic Complications

The structural changes characterising diabetic microangiopathy, which may be referred to as ’abnormal growth’ and ’impaired regeneration’, strongly suggest a role for a number of aberrantly expressed growth factors, possibly acting in combination, in the development of these complications. This initial speculation has been supported by the detection of increased concentrations of several growth factors in the target tissues of diabetic long-term complications, and by enhanced expression of these growth factors consequent to the activation of the biochemical pathways linking hyperglycaemia to microvascular changes: the polyol pathway; non-enzymatic glycation of proteins; vasoactive hormones; oxidative stress, and hyperglycaemic pseudohypoxia. As to nephropathy, insulin-like growth factor I (IGF-I) seems to be implicated in the earlier stages of the disease, while transforming growth factor β (TGFβ) is involved both in the early and later stages, being responsible, at least in part, for extracellular matrix (ECM) accumulation. Vascular endothelial growth factor (VEGF) plays a pivotal role both in non-proliferative and proliferative retinopathy. Finally, deficiency of several neurotrophic factors, namely nerve growth factor (NGF) and IGF-I has been related to the degeneration or impaired regeneration occurring in diabetic neuropathy. Knowledge of the involvement of growth factors in diabetic microangiopathy opens the way to new therapeutic interventions aimed at blocking the deleterious actions of several growth factors.

Enhanced soluble CD40 ligand contributes to endothelial cell dysfunction in vitro and monocyte activation in patients with diabetes mellitus: effect of improved metabolic control

Aims/hypothesisInflammation plays a pathogenic role in the development of accelerated atherosclerosis in diabetes. Soluble CD40 ligand (sCD40L) is enhanced in diabetes; however, the molecular mechanisms linking sCD40L to accelerated atherosclerosis in diabetes are still unclear. We tested the hypothesis that sCD40L may be involved in the vascular complications in diabetes and exerts its effect by triggering inflammatory reactions on mononuclear and endothelial cells (ECs).MethodsWe studied 70 patients, 40 with type 2 and 30 with type 1 diabetes, with a history or physical examination negative for cardiovascular disease, and 40 non-diabetic and 30 healthy subjects, matched with the type 2 and type 1 diabetic patients, respectively. Plasma and serum sCD40L, and plasma soluble intercellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, E-selectin and monocyte chemo-attractant protein-1 (MCP-1) were measured. Adhesion molecules and MCP-1 release, the ability to repair an injury in ECs, and O2− generation in monocytes were analysed in vitro after stimulation with serum from patients or controls.ResultsType 2 and type 1 diabetic patients had significantly higher sCD40L levels than controls. Furthermore, high sCD40L was associated with in vitro adhesion molecules and MCP-1 release, impaired migration in ECs and enhanced O2− generation in monocytes. Improved metabolic control was associated with a reduction of plasma sCD40L by 37.5% in 12 type 1 diabetic patients. Furthermore, elevated sCD40L in diabetic patients was significantly correlated with HbA1c levels.Conclusions/interpretationUpregulation of sCD40L as a consequence of persistent hyperglycaemia in diabetic patients results in EC activation and monocyte recruitment to the arterial wall, possibly contributing to accelerated atherosclerosis development in diabetes.

Oxidative stress in chronic vascular disease: From prediction to prevention.

This review article is intended to describe the strong relationship between oxidative stress and vascular disease. Reactive oxygen species (ROS) play an important role in the pathogenesis of vascular disease: oxidative stress is intimately linked to atherosclerosis, through oxidation of LDL and endothelial dysfunction, to diabetes, mainly through advanced glycation end-products (AGEs)/receptor for AGE (RAGE) axis impairment, protein kinase C (PKC), aldose reductase (AR) and NADPH oxidase (NOX) dysfunction, and to hypertension, through renin–angiotensin system(RAS) dysfunction. Several oxidative stress biomarkers have been proposed to detect oxidative stress levels and to improve our current understanding of the mechanisms underlying vascular disease. These biomarkers include ROS-generating and quenching molecules, and ROS-modified compounds, such as F2-isoprostanes. An efficient therapeutic approach to vascular diseases cannot exclude evaluation and treatment of oxidative stress. In fact, oxidative stress represents an important target of several drugs and nutraceuticals, including antidiabetic agents, statins, renin-angiotensin system blockers, polyphenols and other antioxidants. A better understanding of the relations between atherosclerosis, diabetes, hypertension and ROS and the discovery of new oxidative stress targets will translate into consistent benefits for effective vascular disease treatment and prevention.

Contribution of Platelet-Derived CD40 Ligand to Inflammation, Thrombosis and Neoangiogenesis

CD40-CD40L interactions have been involved in inflammation and thrombosis. Several diseases are characterized by inflammation, hypercoagulability and increased prevalence of thromboembolic events. In the past decade, a series of preclinical and clinical studies has provided more insight into the pathogenetic mechanisms linking inflammatory mediators to the activation and regulation of the haemostatic system. In particular, the study of CD40-CD40L interactions has greatly contributed to understanding the role of platelets in a variety of pathophysiological conditions, including atherothrombosis, immuno-inflammatory diseases and, possibly, cancer. A wide variety of preclinical and clinical studies have generated clinical interest in the use of CD40L as a prognostic marker of thrombotic risk. However, the use of sCD40L in clinical studies requires reliable methods. For the correct interpretation of results, clinical and research laboratories and physicians must be aware of the limitations of immunoassays for this cytokine, which underlines the need for standardization of preanalytic conditions. This review will focus on biochemical evidence of CD40L involvement in platelet activation, contribution of platelet-derived CD40L to inflammation, thrombosis and neoangiogenesis, and possible methodological pitfalls regarding the appropriate specimen and preparation for laboratory evaluation of blood soluble CD40L as a biomarker in various human diseases characterized by underlying inflammation, such as atherothrombosis, cancer and immuno-inflammatory diseases.

Determinants of Increased Cardiovascular Disease in Obesity and Metabolic Syndrome

Obesity is associated with an increased mortality and morbidity for cardiovascular disease (CVD) and adipose tissue is recognised as an important player in obesity-mediated CVD. The diagnosis of the metabolic syndrome (MS) appears to identify substantial additional cardiovascular risk above and beyond the individual risk factors, even though the pathophysiology underlying this evidence is still unravelled. The inflammatory response related to fat accumulation may influence cardiovascular risk through its involvement not only in body weight homeostasis, but also in coagulation, fibrinolysis, endothelial dysfunction, insulin resistance (IR) and atherosclerosis. Moreover, there is evidence that oxidative stress may be a mechanistic link between several components of MS and CVD, through its role in inflammation and its ability to disrupt insulin-signaling. The cross-talk between impaired insulin-signaling and inflammatory pathways enhances both metabolic IR and endothelial dysfunction, which synergize to predispose to CVD. Persistent platelet hyperreactivity/activation emerges as the final pathway driven by intertwined interactions among IR, adipokine release, inflammation, dyslipidemia and oxidative stress and provides a pathophysiological explanation for the excess risk of atherothrombosis in this setting. Despite the availability of multiple interventions to counteract these metabolic changes, including appropriate diet, regular exercise, antiobesity drugs and bariatric surgery, relative failure to control the incidence of MS and its complications reflects both the multifactorial nature of these diseases as well as the scarce compliance of patients to established strategies. Evaluation of the impact of these therapeutic strategies on the pathobiology of atherothrombosis, as discussed in this review, will translate into an optimized approach for cardiovascular prevention.

Plasma levels of soluble CD36, platelet activation, inflammation, and oxidative stress are increased in type 2 diabetic patients

Inflammation, oxidative stress, and platelet activation are involved in type 2 diabetes and its complications. Soluble CD36 (sCD36) has been proposed to early identify diabetics at risk of accelerated atherothrombosis. We aimed at characterizing the platelet contribution to sCD36 in diabetes, by correlating its concentration with the extent of platelet-mediated inflammation and in vivo lipid peroxidation and investigating the effects of low-dose aspirin on these processes. A cross-sectional comparison of sCD36, soluble CD40L (sCD40L) reflecting platelet-mediated inflammation, urinary 11-dehydro-TxB(2), and 8-iso-PGF(2α), in vivo markers of platelet activation and lipid peroxidation, was performed among 200 diabetic patients (94 of them on aspirin 100mg/day) and 47 healthy controls. sCD36 levels (median [IQR]: 0.72 [0.31-1.47] vs 0.26 [0.2-0.37], P=0.003) and urinary 11-dehydro-TxB(2) levels (666 [293-1336] vs 279 [160-396], P≤0.0001) were significantly higher in diabetic patients not on aspirin (n=106) than in healthy subjects. These variables were significantly lower in aspirin-treated diabetics than untreated patients (P<0.0001). Among patients not on aspirin, those with long-standing diabetes (>1 year) had significantly higher sCD36 levels in comparison to patients with diabetes duration <1 year (1.01 [0.62-1.86] vs 0.44 [0.22-1.21], P=0.001). sCD36 linearly correlated with sCD40L (rho=0.447; P=0.0001). On multiple regression analysis, 11-dehydro-TxB(2) (β=0.360; SEM=0.0001, P=0.001), 8-iso-PGF(2α) (β=0.469; SEM=0.0001, P<0.0001), and diabetes duration (β=0.244; SEM=0.207, P=0.017) independently predicted sCD36 levels. sCD36, platelet activation, inflammation, and oxidative stress are increased in type 2 diabetes. Future studies are needed to elucidate if the incomplete down-regulation of sCD36 by low-dose aspirin implies that sCD36 may be derived from tissues other than platelets or if additional antiplatelet strategies in diabetes are necessary to interrupt CD36-dependent platelet activation.

Oxidative-induced membrane damage in diabetes lymphocytes: Effects on intracellular Ca2 + homeostasis

Oxidative stress is linked to several human diseases, including diabetes. However, the intracellular signal transduction pathways regulated by reactive oxygen species (ROS) remain to be established. Deleterious effects of ROS stem from interactions with various ion transport proteins such as ion channels and pumps, primarily altering Ca2 + homeostasis and inducing cell dysfunction. This study characterized the Ca2 + transport system in lymphocytes of patients with type-2 diabetes, evaluating the possible correlation between cell modifications and the existence of specific oxidative stress damage. Lymphocytes from type-2 diabetes patients displayed oxidative stress features (accumulation of some ROS species, membrane peroxidation, increase in protein carbonyls, increase in SOD and Catalase activity) and Ca2 + dyshomeostasis (modified voltage-dependent and inositol 1,4,5-triphosphate-mediated Ca2 + channel activities, decrease in Ca2 + pumps activity). The data support a correlation between oxidative damage and alterations in intracellular Ca2 + homeostasis, possibly due to modification of the ionic control in lymphocytes of type-2 diabetes patients.